A pin-wheel is a mechanical implementation of a tape; it generates a periodic sequence of 0's and 1's. A pin-wheel contains a number L of pins equally spaced around its circumference. The pin-wheel operates, so that
The pin-wheel depicted in Figure 6.17 shows four pin positions without pins. In an actual SZ40, all pin positions had pins, but some were made inactive by folding them down.
The SZ40 had 12 pin-wheels (Fig. 6.18):
We assume that each pin-wheel has an initial position marked by 0.
The key stream k(0), k(1),… was generated according to the following rules:
|KS0.||The set of active pins on a pin-wheel was part of the key variable ...|